Illegal trade in oil, timber or diamonds had to be classed as criminal and prosecuted, Koehler said at the close of the fourth Africa Forum in the Nigerian capital Abuja.

The German president also stressed that as-yet-unexplained issues of raw material exploration were also behind the conflict in the east of the Democratic Republic of Congo.

"Part of the complexity in the east of the Congo is also the question of who wants the commodity, the raw materials and who is exploiting the raw materials and who is behind these exploitations," Koehler said.

"There is no doubt that the international community and the European community is in close contact with African leaders to find out what should be the sustainable solution," he added.

German president hopeful of peaceful end to Congo violence

Koehler, expressed regret that Rwanda's President Paul Kagame had withdrawn from the forum in Abuja but said he was optimistic that the regional meeting on the Congo situation that Kagame was attending instead would "pave the way" for ending the bloodshed in DR Congo.

Kagame, who is considered a crucial figure in efforts aimed at defusing the tension across his country's western border.

The German-African Forum, an initiative of Koehler's brought together leading African and European business and political figures.

"The 21st century demands that we both depend on each other in credibility and should not talk about good governance in a corrupt setting," Koehler said.

Africa, he added, had a right to its own structures and the principles and foundations of its leaders "should not be influenced by the European definition of ideas."

Koehler began a state visit to Nigeria on Monday and over the weekend participated in the Africa Forum where participants agreed on policies to tackle some of Africa's challenges.

The German president listed some of these as poverty, migration and corruption as some of the problems in Africa. He also highlighted Africa's lack of economic development, education and investment.

He said that there was the need for long-term projects to take precedence over short-term ones in African and a more accurate portrayal of the continent by the media.